svn commit: r44724 - head/en_US.ISO8859-1/books/handbook/security
Dru Lavigne
dru at FreeBSD.org
Wed Apr 30 19:31:57 UTC 2014
Author: dru
Date: Wed Apr 30 19:31:56 2014
New Revision: 44724
URL: http://svnweb.freebsd.org/changeset/doc/44724
Log:
Editorial review of 14.2.3 Password Hashes.
Add example of how to view and change the password hash.
Sponsored by: iXsystems
Modified:
head/en_US.ISO8859-1/books/handbook/security/chapter.xml
Modified: head/en_US.ISO8859-1/books/handbook/security/chapter.xml
==============================================================================
--- head/en_US.ISO8859-1/books/handbook/security/chapter.xml Wed Apr 30 19:05:34 2014 (r44723)
+++ head/en_US.ISO8859-1/books/handbook/security/chapter.xml Wed Apr 30 19:31:56 2014 (r44724)
@@ -235,48 +235,84 @@
</sect2>
<sect2 xml:id="security-passwords">
- <title>Passwords</title>
+ <title>Password Hashes</title>
- <para>Passwords are a necessary evil of technology. In the
- cases they must be used, not only should the password be
- extremely complex, but also use a powerful hash mechanism to
- protect it. At the time of this writing, &os; supports
- <acronym>DES</acronym>, <acronym>MD</acronym>5, Blowfish,
- <acronym>SHA</acronym>256, and <acronym>SHA</acronym>512 in
- the <function>crypt()</function> library. The default is
- <acronym>SHA</acronym>512 and should not be changed backwards;
- however, some users like to use the Blowfish option. Each
- mechanism, aside from <acronym>DES</acronym>, has a unique
- beginning to designate the hash mechanism assigned. For the
- <acronym>MD</acronym>5 mechanism, the symbol is a
- <quote>$</quote> sign. For the <acronym>SHA</acronym>256 or
- <acronym>SHA</acronym>512, the symbol is <quote>$6$</quote>
- and Blowfish uses <quote>$2a$</quote>. Any weaker passwords
- should be re-hashed by asking the user to run &man.passwd.1;
- during their next login.</para>
+ <para>Passwords are a necessary evil of technology. When
+ they must be used, they should be
+ complex and a powerful hash mechanism should be used to
+ encrypt the version that is stored in the password database. &os; supports the
+ <acronym>DES</acronym>, <acronym>MD5</acronym>,
+ <acronym>SHA256</acronym>, <acronym>SHA512</acronym>, and Blowfish hash algorithms in its
+ <function>crypt()</function> library. The default of
+ <acronym>SHA512</acronym> should not be changed to a less
+ secure hashing algorithm, but can be changed to the more secure
+ Blowfish algorithm.</para>
<note>
- <para>At the time of this writing, Blowfish is not part of
- <acronym>AES</acronym> nor is it considered compliant with
- any <acronym>FIPS</acronym> (Federal Information
- Processing Standards) standard and its use may not be
+ <para>Blowfish is not part of
+ <acronym>AES</acronym> and is not considered compliant with
+ any Federal Information
+ Processing Standards (<acronym>FIPS</acronym>). Its use may not be
permitted in some environments.</para>
</note>
- <para>For any system connected to the network, two factor
- authentication should be used. This is normally considered
- something you have and something you know. With
- <application>OpenSSH</application> being part of the &os;
- base system and the use of ssh-keys being available for some
- time, all network logins should avoid the use of passwords in
- exchange for this two factor authentication method. For
- more information see the <xref linkend="openssh"/> section of
- the handbook. Kerberos users may need to make additional
+ <para>To determine which hash algorithm is used to encrypt a
+ user's password, the superuser can view the hash for the user
+ in the &os; password database. Each hash
+ starts with a symbol which indicates the type of hash
+ mechanism used to encrypt the password. If
+ <acronym>DES</acronym> is used, there is no beginning symbol.
+ For
+ <acronym>MD5</acronym>, the symbol is
+ <literal>$</literal>. For <acronym>SHA256</acronym> and
+ <acronym>SHA512</acronym>, the symbol is <literal>$6$</literal>.
+ For Blowfish, the symbol is <literal>$2a$</literal>. In this
+ example, the password for <systemitem
+ class="username">dru</systemitem> is hashed using the default
+ <acronym>SHA512</acronym> algorithm as the hash starts with
+ <literal>$6$</literal>. Note that the encrypted hash, not the password
+ itself, is stored in the password database:</para>
+
+ <screen>&prompt.root; <userinput>grep dru /etc/master.passwd</userinput>
+dru:$6$pzIjSvCAn.PBYQBA$PXpSeWPx3g5kscj3IMiM7tUEUSPmGexxta.8Lt9TGSi2lNQqYGKszsBPuGME0:1001:1001::0:0:dru:/usr/home/dru:/bin/csh
+</screen>
+
+ <para>The hash mechanism is set in the user's login class. For
+ this example, the user is in the <literal>default</literal>
+ login class and the hash algorithm is set with this line in
+ <filename>/etc/login.conf</filename>:</para>
+
+ <programlisting> :passwd_format=sha512:\</programlisting>
+
+ <para>To change the algorithm to Blowfish, modify that line to
+ look like this:</para>
+
+ <programlisting> :passwd_format=blf:\</programlisting>
+
+ <para>Then run <command>cap_mkdb /etc/login.conf</command> as
+ described in <xref linkend="users-limiting"/>. Note that this
+ change will not affect any existing password hashes. This
+ means that all passwords should
+ be re-hashed by asking users to run <command>passwd</command>
+ in order to change their password.</para>
+
+ <para>For remote logins, two-factor
+ authentication should be used. An example of two-factor authentication is
+ <quote>something you have</quote>, such as a key, and
+ <quote>something you know</quote>, such as the passphrase for that key. Since
+ <application>OpenSSH</application> is part of the &os;
+ base system, all network logins should be over an encrypted
+ connection and use key-based authentication instead of passwords.
+ For
+ more information, refer to <xref linkend="openssh"/>.
+ Kerberos users may need to make additional
changes to implement <application>OpenSSH</application> in
- their network.</para>
+ their network. These changes are described in <xref
+ linkend="kerberos5"/>.</para>
+ </sect2>
- <sect3 xml:id="security-pwpolicy">
- <title>Password Policy and Enforcement</title>
+ <sect2 xml:id="security-pwpolicy">
+ <title>Password Policy Enforcement</title>
<para>Enforcing a strong password policy for local accounts
is a fundamental aspect of local system security and policy.
@@ -358,7 +394,6 @@ Enter new password:</programlisting>
<para>As seen here, an expiration date is set in the form of
day, month, year. For more information, see
&man.pw.8;</para>
- </sect3>
</sect2>
<sect2 xml:id="security-rkhunter">
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